Bone fixation and fusion device

ABSTRACT

Disclosed is a bone fusion cage that contains bone graft and is implanted between bones in a skeletal system. The cage bears structural loads that are transmitted through the bones of the skeletal system and at least partially shields the contained bone graft from the structural loads. The cage is configured to provide a secondary load to the bone graft independent of the structural load to promote fusion of the bone graft to adjacent bones.

REFERENCE TO PRIORITY DOCUMENT

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/211,160, filed Aug. 23, 2005, which claims the benefit ofpriority of the following co-pending U.S. Provisional PatentApplications: (1) U.S. Provisional Patent Application Ser. No.60/603,809, filed Aug. 23, 2004; (2) U.S. Provisional Patent ApplicationSer. No. 60/670,898, filed Apr. 8, 2005; (3) U.S. Provisional PatentApplication Ser. No. 60/670,899, filed Apr. 8, 2005; (4) U.S.Provisional Patent Application Ser. No. 60/670,900, filed Apr. 8, 2005.Priority of the aforementioned filing dates are hereby claimed, and thedisclosures of the Patent Applications are hereby incorporated byreference herein in their entirety.

BACKGROUND

The present disclosure is directed at skeletal bone fixation systems,components thereof, and methods of implant placement. These devices areused during the surgical reconstruction of skeletal segments to bridgebony gaps and to adjust, align and fixate the remaining bone or bonyfragments

Whether for degenerative disease, traumatic disruption, infection orneoplastic invasion, the surgical resection of bone and the subsequentreconstruction of the skeletal segment is a common procedure in currentmedical practice. Regardless of the anatomical region or the specificsof the individual operation, many surgeons employ an implantable deviceto bridge the region of bone resection and provide structural supportfor the remaining skeletal segment. These devices are especially usefulin spinal surgery where they are used to restore spinal alignment and tostabilize the spinal column after vertebral and/or disc resection.

While these devices provide immediate structural support of theoperative segment, long term stability requires that a bone graft beused to replace the resected bone and that the grafted bone successfullyincorporate (“fuse”) within the skeletal segment. For these reason, manydevices are designed with a rigid outer structure that is intended toprovide immediate stability and a hollow central cavity that is used toretain the bone graft while the bony fusion proceeds.

Unfortunately, this design has a central flaw. In providing stability,the rigid outer structure bears the load transmitted through thatskeletal segment and effectively shields the bone graft from stressforces. Since bone fusion occurs most effectively when the healing boneis subjected to load, placement of the graft within the deviceeffectively shields it from stress forces and leads to a significantreduction in the likelihood of bony fusion. In addition, stressshielding will also significantly diminish the quality and density ofthe fusion mass that will eventually develop.

SUMMARY

In view of the proceeding, it would be desirable to design a fusiondevice without this significant limitation. The new device shouldprovide both rigid support of the reconstructed segment as well as areliable load on the bone graft. This would serve to maximize thelikelihood of bony fusion and optimize the bone quality of the fusionmass.

Disclosed is a fusion device that is especially adapted for thereconstruction of the spinal column. In one aspect, the device comprisesa rigid rectangular body which contains multiple openings. Whenimplanted between two vertebral bodies, the upper end segment abuts thelower surface of the upper vertebra while the lower end segment abutsthe upper surface of the lower vertebra. Each end segment has one ormore central holes that permit contact between the vertebral surface andthe bony fragments within the device center. The cage body providesstructural support for the spinal segment.

The cage has one or more sides that can accommodate a movable side wall.The side wall is positioned within the open portion of the cage and aspring-loaded hinge is placed through the cage and into the side wall.The spring retains the side wall in the closed position.

The cage is threaded onto an insertion handle. The handle is used todeliver the cage into the operative site and also acts to hold themovable side-wall in the open position. Bone fragments are then packedinto the cage center, the cage is placed into the operative site and thehandle is removed. The memory inherent in the spring-loaded hinge willmaintain a constant inward force applied to the healing bone fragments.

The bone fragments within the cage are pushed inwards in a horizontalplane and towards the two end segments in a longitudinal plane. Thelongitudinal component of the force increases the extent of contactbetween the bone graft and the vertebral surfaces whereas bothcomponents apply a constant force onto the graft. Both of these factorsact synergistically to maximize the likelihood of bony fusion andoptimize the quality of the fusion mass.

In another aspect, the fusion cage includes an upper segment, a lowersegment, and a screen that collectively define an interior cavity. Thecage supports a structural load that to the segment of the skeletalsystem in which the bones are located. The screen is configured toexpand outward over a space. The interior cavity can be packed with bonegraft sufficient to cause the screen to expand outwardly over the space.When packed with bone graft, the screen exerts a secondary force on thebone graft.

In another aspect, there is disclosed a bone fusion system, comprising abody sized and shaped for implanting between bones of a skeletal systemand a load member. The body defines an internal cavity configured tocontain bone graft, wherein the body supports a structural loadtransmitted through the bones when implanted in the skeletal system. Theload member that exerts a secondary load onto bone graft containedwithin the internal cavity of the body.

In another aspect, there is disclosed a bone fusion system, comprising acage for implanting between bones of a skeletal system. The cage definesan internal cavity for containing bone graft to be fused with the bones.The cage is configured to bear structural loads transmitted through theskeletal system, wherein at least a portion of the cage is configured toexert a secondary load to the bone graft contained within the internalcavity. The secondary load is separate from the structural load.

In another aspect, there is disclosed a method of fusing a pair of bonesin a skeletal system, comprising: implanting a cage between the pair ofbones such that the cage bears structural loads transmitted through thebones; packing the cage with bone graft, wherein the cage at leastpartially shields the bone graft from the structural loads; and causingthe cage to exert a secondary load to the bone graft contained withinthe cage.

In another aspect, there is disclosed a bone fusion system, comprising acage for implanting between bones of a skeletal system. The cage definesan internal cavity for containing bone graft to be fused with the bones.The cage is configured to bear structural loads transmitted through theskeletal system, wherein the cage is configured to subdivide thestructural load at least by subsidence and exert a secondary load ontothe bone graft contained within the internal cavity.

In another aspect, there is disclosed a method of fusing a pair of bonesin a skeletal system, comprising: Inserting a cage between a pair ofbones; exerting a load onto bone graft contained within an interiorcavity of a fusion cage by advancing an instrument into the interiorcavity at the time of cage insertion to compact, compress and load thebone graft.

The fusion cage device described herein provides rigid support of thereconstructed segment and reliable loading of the bone fragments withinthe cage. These and other features will become more apparent from thefollowing description and certain modifications thereof when taken withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a first embodiment of a cage in anassembled state.

FIG. 2 shows a perspective view of the cage in an exploded state.

FIG. 3 shows a cross-sectional, plan view of the cage with the loadmember in a closed position.

FIG. 4 shows a cross-sectional, perspective view of the cage with theload member in the closed position.

FIG. 5 shows a perspective view of an insertion member positionedadjacent the cage.

FIG. 6 shows an enlarged view of an insertion member positioned adjacentthe borehole of the cage prior to coupling the insertion member to thecage.

FIG. 7 shows an enlarged perspective view of a cage insertion membercoupled to the cage.

FIG. 8 shows cross-sectional, plan view of the cage with the insertionmember coupled thereto.

FIG. 9 shows the cage with the load member in the open position and theinsertion member detached.

FIG. 10 shows another embodiment of a cage.

FIG. 11 shows a perspective view of the cage of FIG. 10 and a loadmember.

FIG. 12 shows a cross-sectional view of the cage of FIG. 10 with a loadmember in a withdrawn position.

FIG. 13 shows a cross-sectional view of the cage of FIG. 10 with a loadmember in an extended position.

FIG. 14 shows a cross-sectional view of the cage coupled to an insertionmember.

FIG. 15 shows an enlarged view of the cage with the load member in thewithdrawn position and with the cage coupled to an insertion member.

FIG. 16 shows an enlarged view of the cage with the load member in theextended position and with the cage coupled to an insertion member.

FIG. 17 shows yet another embodiment of a fusion cage.

FIGS. 18A and 18B show perspective views of a structural core of thecage of FIG. 17.

FIG. 19 shows the mesh screen of the cage of FIG. 17.

FIG. 20 shows an enlarged view of the portion of the screen containedwithin line 19-19 of FIG. 19.

FIG. 21 shows the components of the cage of FIG. 17 prior to assembly.

FIG. 22A shows the cage with the interior cavity empty such that thescreen is in a relaxed position.

FIG. 22B shows a cross-sectional view of the cage with the interiorcavity empty such that the screen is in a relaxed position.

FIG. 23A shows the cage with the interior cavity packed with bone graft.

FIG. 23B shows a cross-sectional view of the cage with the interiorcavity packed with bone graft.

FIG. 24A shows a perspective view of a wedge segment that can be placedagainst the upper or lower segments so as to achieve an inclinedsurface.

FIG. 24B shows a side, cross-sectional view of the wedge segment.

FIG. 25A shows a side, cross-sectional view of the cage with the wedgesegment attached.

FIG. 25B shows a perspective, cross-sectional view of the cage with thewedge segment attached.

FIG. 26 shows a pair of cages positioned atop one another.

FIG. 27 shows yet another embodiment of a fusion cage.

FIG. 28 shows a cross-sectional view of the fusion cage of FIG. 27.

FIG. 29 shows a perspective view of the fusion cage and aninsertion/load system for use with the cage.

FIG. 30 shows an enlarged view of the cage coupled to the insertion/loadsystem.

FIG. 31 shows an enlarged, cross-sectional view of the cage coupled tothe insertion/load system.

FIG. 32 shows another embodiment of a cage and a insertion/load system.

FIG. 33 shows an enlarged view of the cage member and the insertion/loadsystem.

FIG. 34 shows a cross-sectional view of the cage coupled to theinsertion/load system.

DETAILED DESCRIPTION

Disclosed are methods and devices that are adapted to assist in thefusion of adjacent bones of a skeletal system. The methods and devicesare described herein in the context of use in the spine, although thedisclosed methods and devices are suitable for use in any skeletalregion.

The device can be, for example, a cage configured to contain bone graftthat fuses to one or more adjacent bones of a skeletal system in whichthe bones are located. The cage also provides structural support to thesegment of the skeletal system in which the bones are located. In thisregard, the cage bears the structural load that is transmitted throughthe skeletal segment to at least partially shield the contained bonegraft from the structural load. However, the cage is configured toprovide a secondary load (separate from the structural load) to the bonegraft contained within the cage, wherein the secondary load promotesfusion between the bone graft and adjacent bone of the skeletal system.The secondary load contributes to an advantageous increase in density ofthe fusion mass that develops as the bony fusion between the bone graftand adjacent bone proceeds. The secondary load is at least partiallyindependent of the structural load transmitted through the skeletalsystem that the cage supports.

The cage can also be configured to exert at least a portion of thesecondary load to the bones of the skeletal system adjacent the cage.The cage can further be configured so that at least a portion of thestructural load is applied to the bone graft contained within the cage.In this regard, for example, the cage can subdivide the structural loadby subsidence of adjacent bones and exert the secondary load onto thebone graft contained within the cage. The cage can also be configured tofacilitate surface contact between the bone graft within the cage andthe neighboring native bone.

FIG. 1 shows a perspective view of a first embodiment of a cage 100 inan assembled state and FIG. 2 shows a perspective view of the cage 100in an exploded state. The cage 100 is sized and shaped to be implantedbetween an upper vertebra and a lower vertebra of a spine.

The cage 100 includes a main body 105 configured to contain bone graft,at least one load member 110 that provides a load to the contained bonegraft, and a hinge 115 (shown in FIG. 2) that couples the load member110 to the main body 105. The cage 100 is configured to be implantedbetween a pair of bones, such as vertebrae, so as to provide structuralsupport and encourage fusion between the bones and bone graft containedwithin the cage 100. As mentioned, the cage 100 is described herein inan exemplary embodiment where the cage is positioned between twovertebrae, although it should be appreciated that the cage 100 can beused with other bones in a skeletal system.

With reference to FIGS. 1 and 2, the main body 105 has a structure thatis configured to contain bone graft and to be implanted between a pairof vertebrae. The main body 105 can be rectangular-shaped and is made ofa rigid material, such as carbon fiber. The rigidity of the main body105 permits it to provide structural support to the spinal segment inwhich it is implanted.

The main body 105 defines an interior cavity that is at least partiallyexposed via one or more holes or openings disposed in the main body 105,such as on its sides, tops, and/or bottoms. The openings permit contactbetween the vertebral surfaces and the bone graft contained within themain body 105. One of the openings is sized and shaped to receive atleast a portion of the load member 110, as described below.

The main body 105 has an upper region that defines an upper engagementsurface 18 that contacts the upper vertebra when the cage is implantedbetween the vertebrae. The main body 105 further includes a lower regionthat defines a lower engagement surface 120. The upper and lowerengagement surfaces 118, 120 can be flat or can have or regular orirregular-shaped structures thereon, such as having knurled or pyramidalstructures as shown in FIGS. 1 and 2.

A borehole 125 extends through the main body, such as through one of itsside walls. The borehole 125 is sized and shaped to receive an insertionmember, as described in detail below. The borehole 125 can have internalthreads that couple to corresponding threads on the insertion member.

In the embodiment shown in FIGS. 1 and 2, the load member 110 is amoveable side wall that is shaped to complement the shape of the openingin the side of the main body 105. The load member 110 can move in andout of the opening, such as in a rotating or pivoting manner, forexample. In the embodiment shown in FIGS. 1 and 2, the load member 110is door-like and has a substantially rectangular shape that complementsthe shape of the hole in the main body 105. However, the load member 110can have other shapes and structures that are configured to provide aload to bone graft contained within the main body 105, as described inother embodiments below for example. The load member 110 can also beintegrally formed with the main body 105.

As mentioned, the load member 110 is door-like such that it rotatablymoves in and out of the opening in the side of the main body 105. Inthis regard, the load member 110 is coupled to the main body 105 via thehinge 115, which is positioned in a complementary-shaped slot 128 in themain body 105. A portion of the load member 110 is sized and shaped tomate with the slot 128 such that the hinge 115 rotatably retains theload member to the main body 110.

The hinge 115 provides a biasing force that biases the load member 110towards a closed position wherein the load member 110 can apply a loadto bone graft contained within the main body 105. The hinge can be madeof any suitable material and can have any structure and shape thatpermits the hinge 115 to provide such a biasing force. In an exemplaryembodiment, the hinge 115 is made of a thin titanium band that can serveas a spring for biasing the load member 110 toward the main body. Thethin titanium band can also as a radio-opaque marker that can be used toascertain the cage position on an x-ray.

FIG. 3 shows a cross-sectional, plan view of the cage 100 with the loadmember 110 in a closed position. FIG. 4 shows a cross-sectional,perspective view of the cage 100 with the load member 110 in the closedposition. The illustrated embodiment of the load member 110 includes aprojection 305 that extends at least partially into the path of theborehole 125 when the load member is in the closed position. Theprojection 305 forms an abutment surface 310 that is inclined withrespect to the axis of the borehole 125. The projection 305 can be usedin combination with an insertion member to move the load member 110 toan open position, as described below.

At least a portion of the load member 110 extends into the internalcavity of the main body 105 for applying a load to at least a portion ofthe bone graft contained within the main body 105. The load can beapplied by direct or indirect contact between at least a portion of theload member 110 and the contained bone graft, as described below.

FIG. 5 shows a perspective view of an insertion member 505 positionedadjacent the cage 100. The insertion member 505 includes an elongate rodhaving a handle 510 on one end and a cage interface 515 on an oppositeend. The cage interface 515 is configured to removably attach to thecage 515. In an exemplary embodiment, the cage interface 515 is athreaded end portion that removably mates with the threaded borehole 125in the cage 100. FIG. 6 shows an enlarged view of the cage interface 515of the insertion member 505 positioned adjacent the borehole 125 of thecage 100 prior to coupling the insertion member 505 to the cage 100.

The cage interface 515 of the insertion member 505 is threaded into theborehole 125 such that the cage interface 515 gradually moves furtherinto the borehole 125. As the cage interface 515 moves further into theborehole 125, the cage interface 515 forces the load member 110 to movefrom the closed position (shown for example in FIG. 6) into an openposition. In the open position, the load member is withdrawn at leastpartially from the main body 105. FIG. 7 shows an enlarged, perspectiveview of the insertion member 505 coupled to the cage 100 with the loadmember 110 in an open position. Note that the in the open position loadmember 110 is at least partially withdrawn from the main body 105 versusthe closed position (shown in FIG. 6) where the.

The coupling of the insertion member 505 to the cage 100 andcorresponding opening of the load member 110 is described in more detailwith reference to FIG. 8. FIG. 8 shows cross-sectional, plan view of thecage 100 with the insertion member 505 coupled thereto. As the insertionmember 505 is threaded into the borehole 125, the cage interface 515abuts the abutment surface 310 of the projection 305 on the load member505. The continued movement of the cage interface 515 further into theborehole 125 forces the load member outward (as exhibited by the arrow910 in FIG. 9) with respect to the main body 105 and further away fromthe internal cavity defined by the main body 105.

The cage interface 515 can have a length such that an edge of the cageinterface 515 protrudes at least partially into the internal cavity ofthe main body 105. In this manner, the protruding edge of the cageinterface 515 can exert a load on the bone graft that is containedwithin the internal cavity, as describe further below.

In use, the insertion member 505 threaded into the main body 105 tocause the load member 110 to move into the open position such that itwithdraws from the main body 105 of the cage. The insertion member 505acts to hold the load member 110 in the open position. Using theinsertion member 505 as a handle, an operator then implants the cage 100in between a pair of vertebrae, such as between an upper vertebra and alower vertebra. During implantation, an instrument can be advanced intothe internal cavity to compact, compress and load the bone graft.

The internal cavity of the main body 105 is then packed with bone graft.The cavity can be packed with a sufficient volume of bone graft suchthat the bone graft fills the internal cavity.

When positioned between the upper and lower vertebrae, the upper surface118 of the main body 105 abuts or otherwise contacts the upper vertebra.The lower surface 120 abuts or otherwise contacts the lower vertebra.With the cage 100 positioned between the vertebrae, the insertion member505 is detached from the cage 100. FIG. 9 shows the cage 100 with theload member 110 in the open position and the insertion member detached.For clarity of illustration, the upper vertebra and lower vertebra arenot shown. The bone graft contained within the cage 100 is also notshown for clarity of illustration.

With the cage 100 implanted between the vertebrae, the main body 105 ofthe cage 100 provides structural support for the skeletal segment inwhich the upper and lower vertebra are positioned. That is, the cage 100is of sufficient rigidity to bear structural loads that are transmittedthrough the vertebra. The main body 105 of the cage 110 has sufficientrigidity to shield such structural loads from the bone graft containedwithin the main body 105.

Although the main body 105 of the cage 100 shields the contained bonegraft from the structural loads, the load member 110 provides asecondary load to the bone graft contained within the cage 100. When theinsertion member 505 is detached from the cage 100, the cage interface515 (shown in FIG. 9) no longer retains the load member 110 in the openposition. As mentioned, the hinge 115 biases the load member 110 towardthe closed position. Thus, the load member 110 is forced toward theinternal cavity such that the load member 110 exerts a secondary load F1(shown in FIG. 9) onto the bone graft contained within the main body105. As mentioned, secondary load promotes fusion between the bone graftand adjacent bone of the skeletal system.

The bone graft within the cage 100 are pushed inwards in a horizontalplane and towards the upper and lower ends of the cage 100 in alongitudinal plane. The longitudinal component of the force increase theextent of contact between the bone graft and the vertebral surfaceswhereas both components apply a constant force onto the graft. Both ofthese factors act synergistically to maximize the likelihood of bonyfusion and optimize the quality of the fusion mass.

The cage 100 can include holes that extend through the upper and lowerends of the main body 105. When the load member 110 exerts the loadagainst the bone graft contained within the main body, the bone graftcan be urged to move upward and/or downward through the upper and lowerholes. The force can urge the bone graft upward and downward out of theholes toward the upper and lower vertebra. In this manner, the bonegraft is urged into increased surface contact with the neighboringbones. This promotes fusion between the bone graft and the neighboringbones.

FIG. 10 shows another embodiment of a cage, which is referred to as cage1000. The cage 1000 comprises a rectangular body 1005 having boreholesthat extend through a sidewall. The boreholes includes a couplerborehole 1015 that is configured to receive an insertion member, asdescribed below. A pair of load member boreholes 1020 a and 1020 b arealso located on the sidewall. The load member boreholes 1020 a, 1020 bmate with a pair of extensions 1012 on a load member 1010.

The load member 1010 is shown in FIG. 11, which shows an exploded viewof the cage 1000. The load member 1010 is a wall 1018 having a pair ofextensions 1012 extending therefrom. The extensions 1012 are sized andpositioned to fit within the load member boreholes 1020. FIG. 12 shows across-sectional view of the cage 1000 with the load member mounted inthe load member boreholes 1020 with the load member in a withdrawnposition. The extensions 1012 are frustoconical in shape and fit withinthe boreholes 1010 in a press-fit fashion. Each borehole 1020 includes ashoulder 1025 along its length.

With reference to FIG. 13, the load member 1000 can be pushed into anextended position wherein the load member 1000 is positioned furtherinside the internal cavity of the cage 1000. The load member 1000 ismoved inwardly relative to the body 1005 of the cage 1000 such that theextensions 1012 slide inwardly through the boreholes 1020. Theextensions 1012 are configured to expand when they move past theshoulders 1025 such that the expand radially—outward once they move pastthe shoulders 1025. The edges of the extensions in combination with theshoulders 1025 thereby act as a detent to prevent the load member 1010from sliding back in the outward direction through the boreholes 1020.

FIG. 14 shows a cross-sectional view of the cage 1000 coupled to aninsertion member 1405. The insertion member includes an elongate rodhaving a handle at one end and a cage interface at an opposite end thatremovably mates with the borehole 1015 (shown in FIG. 10) of the cage1000. The insertion member 1405 has an axial bore that is sized toreceive a load member actuator 1410 that can be used to move the loadmember 1010 from the withdrawn position to the extended position. Theload member actuator 1410 is an elongate rod having a length sufficientto be inserted entirely through the insertion member 1405.

The manner in which the load member actuator 1410 moves the load member1010 from the withdrawn position to the extended position is nowdescribed with reference to FIGS. 15 and 16. FIG. 15 shows an enlargedview of the cage 1000 with the load member in the withdrawn position andwith the cage coupled to the insertion member 14015. The load memberactuator 1410 is located within the insertion member 1405 with a distalend 1505 of the actuator 1410 spaced from the load member 1010.

To move the load member 1010 to the extended position, the load memberactuator 1410 is pushed toward the load member 1010 such that the distalend 1505 of the actuator 1410 abuts the load member 1010. The loadmember actuator 1410 pushes the load member 1010 into the extendedposition, as shown in FIG. 16.

In use, the cage 1000 is positioned between a pair of vertebrae usingthe insertion member 1405, such as in the manner described above withrespect to the previous embodiment. The cage 100 is then packed withbone graft while the load member is in the withdrawn position, as shownin FIG. 15. The load member actuator 1410 is then used to move the loadmember 1010 to the extended position. As the load member 1010 moves intothe extended position, it exerts a load onto the bone graft containedwithin the cage. Advantageously, the main body 1005 of the cage 1000supports structural loads of the skeletal system while the load member1010 exerts a secondary load on the bone graft contained within thecage.

FIG. 17 shows yet another embodiment of a fusion cage, referred to ascage 1700, which includes a rigid structural core 1705 and a load membercomprised of a mesh screen 1708 that is coupled to the core 1705.

FIGS. 18A and 18B shows upper and lower perspective view of the core1705. The core 1705 includes three elongate struts including a mainstrut 1710 and a pair of secondary struts 1715, and 1720. The struts1710, 1715, 1720 support a pair of end segments, including an uppersegment 1725 and a lower segment 1730. The strut 1710 has an internalaxial bore with internal walls that can include threads.

With reference still to FIGS. 18A and 18B, the upper segment 1725 can beshaped like the vertebral end plate it is designed to rest against. Theupper segment has one or more radially-extending portions that connectto a peripheral portion so as to form one or more holes through theupper segment 1725. In an exemplary embodiment, the segment 1725includes a full thickness bore 1810 with a tapered opening, wherein thebore 1810 overlies the upper end the strut 1710 in the assembled device.The upper segment 1725 can include indentations (such as pyramidalindentations) on an upper surface, wherein the indentations rest againstthe lower surface of the upper vertebra.

FIG. 18B shows the underside of the upper segment 1725. A lip 1815extends downwardly along the periphery of the upper segment 1725. Thelip 1815 accommodates the mesh screen 1708 (shown in FIG. 17) of thecage 1700, as described below.

With reference to FIGS. 18A and 18B, the lower segment 1730 can also beshaped like the vertebral end plate it is designed to rest against. Thelower segment 1730 has one or more radially-extending portions thatconnect to a peripheral portion so as to form one or more holes throughthe lower segment 1730. A full thickness bore 1825 (shown in FIG. 188)without a tapered opening overlies the lower end of the strut 1710. Thelower segment 1730 can include indentations (such as pyramidalindentations) on a lower surface, wherein the indentations rest againstthe upper surface of the lower vertebra.

FIG. 18A shows the upper side of the lower segment 1730. A lip 1818extends upwardly along the periphery of the lower segment 1730. The lip1818 accommodates the mesh screen 1708 (shown in FIG. 17) of the cage1700, as described below.

The indentations on the upper and lower segments can be similarly-shapedbut staggered. The staggered configuration permits two cages 1700 (anupper cage and lower cage) to staked on top of one another such that thepyramidal indentations of the lower end segment of the upper cagecompliment the upper end segment of the lower cage. While the individualsegments have been separately described, the cage 1700 can be a unitarydevice that is manufactured as one piece.

FIG. 19 shows the mesh screen 1708 of the cage 1700. The screen 1708couples to the core 1705 to define an interior cavity that can containbone graft. The screen 1708 defines an outer peripheral shape thatsubstantially corresponds to the outer periphery of the segments 1725and 1730. The screen 1708 defines a plurality of full thickness openings1905, which may be of any geometric shape and occupy the total surfacearea of the screen 1708 or only a part of the screen 1708. In analternate embodiment, the Screen 1708 is solid.

The screen 1708 is a planar piece of material that is wrapped arounditself in an annular fashion. The screen 1708 has a pair of edges 1915and 1920 that overlap one another and that can be drawn apart from oneanother so as to permit a predefined amount of expansion when theinterior cavity is packed with bone graft. FIG. 20 shows an enlargedview of the portion of the screen 1708 contained within line 19-19 ofFIG. 19. As mentioned, the edges 1915 and 1920 overlap with one another.In one embodiment, the edge 1915 has a tapered thickness.

Any of the cages described herein or any of their components can be madeof any biologically adaptable or compatible materials. Materialsconsidered acceptable for biological implantation are well known andinclude, but are not limited to, stainless steel, titanium, tantalum,combination metallic alloys, various plastics, resins, ceramics,biologically absorbable materials and the like. It would be understoodby one of ordinary skill in the art that any system component can bemade of any materials acceptable for biological implantation and capableof withstanding the load encountered during use. Any components may befurther coated/made with osteo-conductive (such as deminerized bonematrix, hydroxyapatite, and the like) and/or osteo-inductive (such asTransforming Growth Factor “TGF-B,” Platelet-Derived Growth Factor“PDGF,” Bone-Morphogenic Protein “BMP,” and the like) bioactivematerials that promote bone formation.

Further, any instrument or device used in implant placement may be madefrom any non-toxic material capable of withstanding the load encounteredduring use. Materials used in these instruments need not be limited tothose acceptable for implantation, since these devices function todeliver the implantable segments but are not, in themselves, implanted.

FIG. 21 shows the components of the cage 1700 prior to assembly. Duringassembly of the device, the edges 1915 and 1920 of the screen 1708 arepulled apart from one another a distance sufficient to clear strut 1710.The screen 1708 is then inserted over and around the strut 1710 and thenrotated into position. The screen 1708 is bounded on an outer surface bythe upwardly and downwardly extending lips 1818 and 1815 (shown in FIGS.18A and 18B) on the lower and upper segments. When in place, the screen1708 can be retained by attachment to back end of the strut 11710 usingany applicable technique that is acceptable for joining segments ofthose particular materials used for manufacture.

FIG. 22A shows the cage 1700 with the interior cavity empty such thatthe screen 1708 is in a relaxed position. FIG. 22B shows across-sectional view of the cage 1700 with the interior cavity emptysuch that the screen 1708 is in a relaxed position. When the cage 1700is empty and the screen 1708 in the relaxed position, a space 2205exists between the struts 1715, 1720 and the outer surface of the screen1708. The space 2205 is for outward expansion of the screen 1708 whenthe interior cavity is filled with bone graft.

The interior cavity can be packed with bone graft sufficient to causethe screen 1708 to expand outwardly over the space 2205. FIG. 23A showsthe cage 1700 with the interior cavity packed with bone graft. FIG. 23Bshows a cross-sectional view of the cage 1700 with the interior cavitypacked with bone graft. (For clarity of illustration, the bone graft isnot shown in FIGS. 23A and 23B.) Note that the bone graft has caused thescreen 1708 to expand outward against the struts 1715, 1720 such thatthe space 2205 (shown in FIGS. 22A, 22B) is no longer present. It shouldbe appreciated that the screen 1708 is biased inwardly such that itexerts a radially-inward load against the bone graft contained in theinterior cavity of the cage 1700.

In the embodiment shown in FIGS. 17-23, the upper and lower segments1725 and 1730 have outer surfaces that are parallel. It should beappreciated that the surfaces of the segments 1725 and 1730 can benon-parallel or contoured so as to conform to, complement, or otherwiserecreate the curvature of the spinal segment they are intended toreconstruct.

FIG. 24A shows a perspective view of a wedge segment 2410 that can beplaced against the upper or lower segments so as to achieve an inclinedsurface. FIG. 248 shows a side, cross-sectional view of the wedgesegment 2410. The wedge segment has a bottom surface that can engage theupper surface of the upper segment 1725. The wedge segment furtherincludes an upper surface that is inclined. The segment includes upperholes 2420.

Pyramidal indentations or other type of alignment structures arepositioned along the upper, oblique surface that is intended to restagainst the lower surface of the upper vertebra. Pyramidal indentationsare also located along the straight bottom surface and interact with andcompliment the indentations on the upper surface of the upper segment1725.

A full thickness bore 2425 with a tapered opening extends through thewedge segment 2410 and aligns with the bore 1810 (shown in FIG. 18A) onthe upper segment 1725 when the wedge segment 2425 is positioned atopthe upper segment 1725

FIG. 25A shows a side, cross-sectional view of the cage 1700 with thewedge segment 2410 attached. FIG. 25B shows a perspective,cross-sectional view of the cage 1700 with the wedge segment 2410attached. An elongate screw 2505 extends through the axial bore in thestrut 1710. The screw 2505 can include threads that mate with threadsinside the axial bore in the strut 1710.

The screw 2505 functions to retain the wedge segment 2410 on top of thecage 1700. In this regard, the screw 2505 has an enlarged head 2510 thatabuts the upper end of the wedge segment 2410 to retain the wedgesegment 2410 in place. The head can include indentation, which isintended to receive an engageable driver. While depicted as a hexagonalindentation, it is understood that any engageable head design andcomplimentary driver may be used.

FIG. 26 shows a pair of cages 1700 positioned atop one another to form adevice of greater total length. Since individual cages can bemanufactured in any variety of lengths, the ability to combine more thanone cage greatly expands the number of overall lengths available to theuser. Because the pyramidal indentations are staggered relative to oneanother, they compliment and interlock with one another when two cagesare stacked. A screw 2610 similar to the screw 2510 (but longer) is usedto hold the stacked devices together.

While not illustrated, a wedge segment 2410 may be added to the top ofthe stacked cages so that the end segments of the total device are notparallel. Alternatively, the top surface of the upper device can be madeat an inclined angle. The lower surface of the lower device can alsomade at an inclined angle. In this way, the total (stacked) device canbe made with non-parallel upper and lower surfaces.

In use, a distraction instrument is used to grab the screen 1708 of anempty cage 1700. The openings 1905 (shown in FIG. 19) can be used tograb hold of the screen 1708. The instrument applies a distraction forceacross the open end of the screen 1708 thereby opening it. Thedistraction force is maintained while the interior cavity of the cage1700 is packed with bone graft, such as through the openings in theupper or lower end segments.

The distraction instrument is used to hold and guide the packed cage1700 into the operative site and properly position it, such as betweenan upper vertebra and a lower vertebra. At this stage, theradially-inward force exerted by the bias of the screen 1708 iscountered by the distraction instrument such that the bone graft doesnot experience any compressive force from the screen 1708. However, thebone fragments are retained within the cage 1700 by the force used topack them into the cage 1700.

Once the cage 1700 is properly positioned between the vertebra, thedistraction instrument is released and the same instrument is used tocompress the screen edges. In this way, a centripetal, compressive forceis applied to the bone graft inside the cage 1700 and the force ismaintained by the memory inherent in the material used to manufacturethe screen 1708. The applied force will also drive the bone graft withinthe cage 1700 towards the upper and lower end and increase the contactbetween the caged bone and the vertebral bone.

FIG. 27 shows a perspective view of a cage 2700 that includes acylindrical outer wall that defines an interior cavity. As shown in thecross-sectional view of FIG. 28, the interior cavity of the cage 2700 isenclosed at one end by a wall and open at an opposite end. Threads 2805are located in the interior of the outer wall at the opening to theinterior cavity.

FIG. 29 shows a perspective view of an insertion member 2905 and a loadmember 2910 for use with the cage 2700. The insertion member 2905 is anelongate road having an internal shaft 2015 that receives the loadmember 2910. As shown in the enlarged view of FIG. 30, an end of theinsertion member 2905 includes coupling members, such as tabs 3005 thatmate with coupling members, such as complementary-shaped notches 3010(shown in FIGS. 27 and 28), in the cage 2700. The tabs 3005 can be matedwith the notches 3010 to removably couple the insertion member 2905 tothe cage 2700.

The cage 2700 is packed with bone graft and implanted between a pair ofbones using the insertion member 2905. When the insertion member 2905 iscoupled to the cage 2700, the load member 2910 is inserted into theshaft 2015 such that the end of the load member 2910 protrudes out ofthe insertion member 2905 and into the internal cavity of the cage 2700,as shown in FIG. 31. The end of the load member 2910 has threads thatmate with the threads inside the cage 2700. The load member 2910 is thenthreaded downwardly so that it protrudes further into the internalcavity of the cage 2700. The end of the load member 2910 can be used toexert a load onto bone graft that has been packed into the internalcavity of the cage 2700. In this manner, a secondary load can be exertedonto the graft during insertion of the cage between bones.

FIG. 32 shows yet another embodiment of a cage 3200 and aninsertion/load system that includes an insertion member 3205 and a loadmember driver 3215. The cage 3200 is similar to the cage 2700 describedabove, although the cage 3200 includes a load member 3210 comprised of anut that having external threads that mate with the threads in theopening of the cage 3200.

As shown in FIG. 33, the insertion member 3205 has coupling members(such as tabs) that mate with coupling members (such as notches) in thecage 3200. The load member 3210 has a cavity 3305 or other couplingmeans that mates with a driver 3310 (such as a hexagonal extension) onthe end of the load member driver 3215.

FIG. 34 shows a cross-sectional view of the cage 3200 coupled to theinsertion member 3205 and the load member driver 3215. The driver 3310is inserted into the cavity 3305 in the load member 3210. The driver3310 can be rotated to cause the load member 3210 to move further intothe internal cavity in the cage 3200 such that the load member 3210exerts a secondary load on bone graft contained within the cage 3200.That is, the load member 3210 compressed bone graft within the cavity.In an alternative embodiment, the load member 3210 is spring-loaded suchthat it is biased toward the internal cavity to exert a constant loadonto bone graft contained within the internal cavity.

Although embodiments of various methods and devices are described hereinin detail with reference to certain versions, it should be appreciatedthat other versions, embodiments, methods of use, and combinationsthereof are also possible. Therefore the spirit and scope of theappended claims should not be limited to the description of theembodiments contained herein.

1-6. (canceled)
 7. A method of using a fusion implant to reconstruct adefective portion within a spinal segment of a subject, the spinalsegment comprising a superior vertebral bone, an inferior vertebral boneand an intervening intervertebral disc space, and the defective portionextending from an inferior aspect of the superior vertebral bone to asuperior aspect of the inferior vertebral bone and disruptingtransmission of a vertical load along a longitudinal axis of the spinalsegment, the method comprising: coupling an implant placement assemblyto a proximal side wall of the fusion implant, the fusion implantcomprising: (i) an upper abutment member configured to abut the inferioraspect of the superior vertebral and comprising a least one feature thatis configured to increase fixation of the fusion implant onto bone, (ii)a lower abutment member configured to abut the superior surface of theinferior vertebral, the lower abutment member positioned a firstdistance from the upper abutment surface; (iii) a distal side wallpositioned opposite the proximal wall, the distal side wall and theproximal side wall being separated by a second distance when measuredalong a second axis; (iv) an internal cavity positioned at leastpartially between the proximal side wall and the distal side wall; and(v) a load member that is movable relative to the proximal side wall andconfigured to transition from a first position to a second position atleast partially within the internal cavity; placing a bone formingmaterial within the internal cavity of the fusion implant; positioningthe fusion implant at least partially within the defective portion, suchthat the upper abutment member of the fusion implant abuts the inferioraspect of the superior vertebral bone and the lower abutment member ofthe fusion implant abuts the superior aspect of the inferior vertebralbone, the positioning causing at least a portion of the vertical load tobe transmitted through the fusion implant; and using a displacementinstrument to transition the load member from the first position to thesecond position; wherein the transitioning the load member from thefirst position to the second position causes at least: (i) a decrease ofa distance between the load member and the distal side wall along thedirection of the second axis while the first distance and the seconddistance remain unchanged, and (ii) the load member to apply acompressive force onto the bone forming material contained in theinternal cavity.
 8. The method of claim 7, further comprisingdisengaging the displacement instrument from the fusion implant afterthe transitioning the load member from the first position to the secondposition has been completed.
 9. The method of claim 8, wherein after thedisengaging the displacement instrument has been completed, the loadmember is retained at a distance from the distal side wall, as measuredalong the direction of the second axis, which is reduced relative to adistance from the side wall when in the load member was in the firstposition.
 10. The method of claim 7, wherein the compressive forceapplied by the load member comprises a load component extending along adirection that is non-parallel to the longitudinal axis of the spinalsegment.
 11. The method of claim 7, wherein the compressive forceapplied by the load member comprises a vertical load component, thevertical load component extending along a direction which is at leastapproximately parallel to the longitudinal axis of the spinal segment.12. The method of claim 7, wherein the placing the bone forming materialwithin the internal cavity of the fusion implant occurs prior to thepositioning the fusion implant at least partially within the defectiveportion.
 13. The method of claim 7, wherein the placing the bone formingmaterial within the internal cavity of the fusion implant occurs whilethe implant placement assembly is coupled to the proximal side wall ofthe fusion implant.
 14. The method of claim 7, wherein the placing thebone forming material within the internal cavity of the fusion implantoccurs subsequent to completion of the positioning the fusion implant atleast partially within the defective portion.
 15. The method of claim 7,wherein implant attachment assembly further comprises the displacementinstrument.
 16. The method of claim 7, wherein the using thedisplacement instrument to transition the load member from the firstposition to the second position comprises using the displacementinstrument to transition while the implant placement assembly is coupledto the fusion implant.
 17. The method of claim 7, wherein thepositioning the fusion implant at least partially within the defectiveportion comprises positioning the fusion implant such that the loadmember does not bear at least a portion of the vertical load transmittedfrom the superior vertebral bone to the inferior vertebral bone andthrough the fusion implant.
 18. The method of claim 7, wherein thefusion implant further comprises a coupling member providing a biasingforce on the load member towards the second position of the load member,and wherein the using the displacement instrument to transition the loadmember from the first position to the second position comprises at leastusing the biasing force.
 19. The method of claim 7, wherein the fusionimplant further comprises a mechanism configured to bias the load membertowards the second position.
 20. The method of claim 7, furthercomprising preloading the load member with a biasing force, the biasingforce urging transition of the load member from the first position tothe second position.
 21. The method of claim 7, wherein: the fusionimplant comprises a non-expandable device; and the second distancecomprises a fixed distance.
 22. A method of using a fusion implant toreconstruct a defective portion within a spinal segment of a subject,the spinal segment comprising a superior vertebral bone, an inferiorvertebral bone and an intervening intervertebral disc space, wherein thedefective portion extends from an inferior aspect of the superiorvertebral bone to a superior aspect of the inferior vertebral bone anddisrupts transmission of a vertical load along a longitudinal axis ofthe spinal segment, the method comprising: coupling an implant placementassembly to the fusion implant, the fusion implant comprising: (i) anupper abutment member configured to abut the inferior aspect of thesuperior vertebral and comprising a least one feature configured toincrease fixation of the upper abutment member onto bone, (ii) a lowerabutment member configured to abut the superior surface of the inferiorvertebral and positioned a first distance from the upper abutmentsurface; (iii) a distal side wall positioned opposite a proximal sidewall, the distal side wall and the proximal side wall being separated bya second distance when measured along a second axis; (iv) an internalcavity positioned at least partially between the proximal side wall andthe distal side wall; and (v) a load member configured to transitionfrom a first position to a second position at least partially within theinternal cavity; inserting a bone forming material within the internalcavity of the fusion implant; positioning the fusion implant at leastpartially within the defective portion, such that the upper abutmentmember of the fusion implant abuts the inferior aspect of the superiorvertebral bone and the lower abutment member of the fusion implant abutsthe superior aspect of the inferior vertebral bone, the positioningcausing at least a portion of the vertical load to be transmittedthrough the fusion implant; and using at least the displacementinstrument, transitioning the load member from the first position to thesecond position while the implant placement assembly is coupled to thefusion implant; wherein the act of transitioning the load member fromthe first position to the second position: (i) decreases a distancebetween the load member and the distal side wall of the fusion implantalong the second axis while the first distance and the second distanceremain unchanged, and (ii) causes the load member to apply a compressiveforce onto the bone forming material contained in the internal cavity.23. The method of claim 22, further comprising disengaging thedisplacement instrument from the fusion implant after the transitioningthe load member from the first position to the second position has beenperformed.
 24. The method of claim 23, wherein after the disengaging thedisplacement instrument is performed, the load member is retained at alesser distance from the distal side wall, as measured along thedirection of the second axis, than the distance of the load member fromthe distal side when the load member in the first position.
 25. Themethod of claim 22, wherein the compressive force applied by the loadmember comprises an at least partly transverse load component, the atleast partly transverse load component extending along a direction thatis non-parallel to the longitudinal axis of the spinal segment.
 26. Themethod of claim 22, wherein the compressive force applied by the loadmember comprises a vertical load component, the vertical load componentextending along the direction of the longitudinal axis of the spinalsegment.
 27. The method of claim 22, wherein the inserting the boneforming material within the internal cavity of the fusion implant isperformed prior to the positioning the fusion implant at least partiallywithin the defective portion.
 28. The method of claim 22, wherein theinserting the bone forming material within the internal cavity of thefusion implant is performed while the implant placement assembly iscoupled to the fusion implant.
 29. The method of claim 22, wherein theinserting the bone forming material within the internal cavity of thefusion implant is performed subsequent to the positioning the fusionimplant at least partially within the defective portion.
 30. The methodof claim 22, wherein the positioning the fusion implant at leastpartially within the defective portion comprises positioning the fusionimplant such that the load member does not bear that portion of thevertical load transmitted from the superior vertebral bone to theinferior vertebral bone and through the fusion implant.
 31. The methodof claim 22, wherein the fusion implant further comprises a mechanismconfigured to cause biasing of the load member towards the secondposition.
 32. The method of claim 31, further comprising preloading theload member with a biasing force, the biasing force easing transition ofthe load member from the first position to the second position.
 33. Themethod of claim 22, wherein the load member comprises a curvilinearconfiguration, and wherein the transition of the load member from thefirst position to the second position comprises utilizing at least aportion of the curvilinear configuration.
 34. The method of claim 22,wherein the transitioning the load member from the first position to thesecond position comprises causing the load member to apply a centripetalforce onto the bone forming material, the centripetal force being atleast partially directed towards a vertical axis of the spinal segment.35. The method of claim 22, wherein: the fusion implant comprises anon-expandable, rectangular body having the proximal side wall, thedistal side wall, a first side wall connecting the proximal side walland the distal side wall, and a second side wall opposing the first sidewall; and the positioning the fusion implant at least partially withinthe defective portion, such that the upper abutment member of the fusionimplant abuts the inferior aspect of the superior vertebral bone and thelower abutment member of the fusion implant abuts the superior aspect ofthe inferior vertebral bone comprises maintaining a relationship betweenthe first sidewall and second sidewall at least during said positioning.36. The method of claim 22, wherein the load member is configured tomove relative to each of the proximal side wall, the distal side wall,the first side wall and the second side wall, and wherein thetransitioning the load member from the first position to the secondposition comprises causing said movement relative to each of theproximal side wall, the distal side wall, the first side wall and thesecond side wall.